Field of the Invention
The invention relates to a device for feeding sheets to a sheet-processing machine, in particular to a printing machine having a reciprocating pregripper that receives the sheets from a feeding table and transfers them to a feed drum of the sheet-fed rotary printing machine.
The problem with such sheet transportation, in particular in the case of sheets which have already been printed at least once beforehand, is that these sheets may be scratched or smudged by contact with the provided transporting and aligning equipment. Furthermore, at high operating speeds, the sheets tend to form so-called infeed buckling (caused by a change in curvature of the transporting path), in the case of which the end of the sheet rises up on the feed drum and, upon detachment from the feed drum, causes a by no means inconsiderable level of noise, and possible damage to the sheet.
The published German Patent Document DE 43 22 416 A1 discloses a feeding table of which an imaginary extension intersects the periphery of a feed drum. A pregripper disposed so as to be swingable beneath the conveying plane transports the sheet on a circular sheet-movement path about a swivel point of the swing axis of the pregripper.
As it is swivelled back to the feeding table, the pregripper passes through the conveying plane of the sheet. In order to avoid contact between the pregripper and the sheet, however, swivellably arranged directing elements are provided for lifting the sheet so high that the sheet does not come into contact with the pregripper. Uniform sheet guidance is thereby disrupted.
A further disadvantage with respect to the aforementioned published German Patent Document DE 43 22 416 A1 is that an infeed gap between the sheet-directing element and the feed cylinder becomes smaller due to the lifting of the sheet-directing element. Furthermore, the sheet that is to be transported is curved additionally in the sheet-movement path.
It is accordingly an object of the invention to provide a device for feeding sheets to a sheet-processing machine with which a uniform sheet-movement path is produced.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for driving a pregripper having a swivellably mounted main lever and a swivellably mounted guide lever, and a gripper bar mutually coupling the main lever and the guide lever, comprising a cyclical swivel drive for the main lever, and an eccentrically swivellable bearing location for the guide lever.
In accordance with another feature of the invention, the driving device includes a feed table, and an imaginary extension of the feed table spaced a given distance from a periphery of a feed drum.
In accordance with a further feature of the invention, during a transporting movement of a sheet from the feed table to gripper devices of the feed drum, a movement path is describable by the pregripper differing from that of a return movement thereof back to the feed table from a turning position of the pregripper.
In accordance with an added feature of the invention, during the transporting movement of the sheet from the feed table to the gripper devices of the feed drum, the sheet is movable by the pregripper into an infeed gap defined by an imaginary extension of the feed table and a periphery of the feed drum, the pregripper, during the return movement thereof, being movable back beneath the imaginary extension of the feed table.
In accordance with an additional feature of the invention, the pregripper has a first cam gear mechanism for swivellingly moving the main lever, and a second cam gear mechanism for swivellingly moving the gripper bar.
In accordance with yet another feature of the invention, the first cam gear mechanism is connected to a couple by the main lever, and the second cam gear mechanism is connected to the couple by the guide lever.
In accordance with yet a further feature of the invention, an articulated point of the main lever on the couple is a gripper shaft of a gripper of the pregripper.
In accordance with yet an added feature of the invention, the driving device includes fixedly disposed directing brackets.
In accordance with yet an additional feature of the invention, the directing brackets are spaced apart a given distance from the feed drum of the feed table.
In accordance with still another feature of the invention, the given distance between the directing brackets and the feed drum is at most equal to a distance between an imaginary extension of the feed table and the feed drum.
In accordance with still a further feature of the invention, the driving device includes a sensor and an actuator for correcting incorrect movements of the pregripper.
In accordance with still an added feature of the invention, the driving device includes a roller lever for deflecting the guide lever, the roller lever having a variable length between the cam roller and the swivellable bearing location of the guide lever.
In accordance with still an additional feature of the invention, the roller lever is formed of two swivellable levers having a common swivel point.
In accordance with another feature of the invention, the swivellable levers are mutually coupled by an actuator.
In accordance with a further feature of the invention, one of the swivellable levers is articulated on the guide lever, and the other of the swivellable levers bears the cam roller.
In accordance with an added feature of the invention, the driving device includes a sensor for determining incorrect movements of the pregripper, and a signalling device for emitting correction signals to an actuator.
In accordance with an additional feature of the invention, the driving device includes an actuator disposed between a framework-fixed bearing point and a stop of the roller lever.
In accordance with yet another feature of the invention, the actuator is capable of receiving correction signals as a function of incorrect movements of the pregripper which have been determined by a sensor.
In accordance with yet a further feature of the invention, the sensor is disposed on a feed drum.
In accordance with yet an added feature of the invention, the sensor is disposed on a structural feature selected from the group consisting of a feed drum, a feed table and the pregripper.
In accordance with a concomitant feature of the invention, the sensor is disposed in a stationary manner.
An advantage of the invention is that, on the swivelling path from the feed cylinder to the feed table, the pregripper describes a different movement path, which is located beneath the sheet-feeder. A result thereof is that the following sheet does not come into contact with the gripper that is swivelling or pivoting back, and thus is also not scratched.
A further advantage of the invention is that the imaginary extension of the feed table is at a distance from the feed drum. This measure prevents the situation wherein the sheet drawn off from the feed table by the gripper device, which is provided on the feed cylinder, forms so-called infeed buckling. Furthermore, the infeed path is curved to a lesser extent, with the result that, as the sheet is fed in, the sheet deforms to a lesser extent and is thus also fed with fewer markings thereon.
In a favorable configuration of the invention, a cam gear mechanism and an eccentric gear mechanism, which are coupled to one another, are provided for the purpose of achieving the movement geometry according to the invention. Stationary directing brackets which are provided define clear separation of the movement paths. The pregripper advantageously comprises a main lever that pivots or swivels about a framework-fixed pivot or swivel point, and a guide lever that swivels or pivots about an eccentrically swivellable or pivotable swivel or pivot point. A couple that bears the gripper bar connects the guide lever and the main lever.
In order to conserve or economize on moved masses, the gripper shaft may be arranged coaxially with the bearing location of the main lever and the couple.
A further advantage is to provide sensors and actuators which monitor and correct incorrect movements of the pregripper. This measure ensures higher-quality sheet transportation.
A further development, for the purpose of correcting incorrect movements, makes provision for arranging an actuator in a roller lever that is connected in an articulated manner to the guide lever. This allows the couple or coupling link, or the gripper bar to be pivoted or swivelled relative to the main lever, with the result that it is possible to correct the position of the sheet in the circumferential direction during transportation by way of the pregripper.
In the case of another exemplary embodiment, the actuator is mounted on the framework and, in the event of correction, displaces a stop for the roller lever so that the cam roller lifts off from the cam. A sensor senses or determines actual-value deviations in the transfer path of the pregripper from the feed table up to the transfer to the feed drum, and provides the actuators with the determined correction data.
In this regard, it is also possible for the sensor to be arranged in a stationary manner on the feed table, with the result that a distance between the pregripper and the feed table can be sensed or determined and corrected by the actuator. Supply lines to the stationary sensor may likewise advantageously be laid in a stationary manner, with the result that the service life of each of the supply lines is improved.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for feeding sheets to a sheet-processing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: